1. Field of the Invention
The present invention relates to a flow cell for a particle analyzer using an electrical sensing zone method. More particularly, it relates to a flow cell for a particle analyzer that employs, for the measurement in size and number of powdery particles such as fine ceramic particles, pigments and cosmetic powders, an electrical sensing zone method in which a particle containing liquid is passed through an aperture so that particles in the liquid are measured based on changes in electrical impedance, and a so-called sheath flow method in which a flow of the particle containing liquid is enclosed by a sheath liquid to pass through the aperture.
2. Description of Related Art
The electrical sensing zone method has been utilized to measure in size and number of blood cells in blood or industrial particles such as cement powders, latexes and toners. In this method, a barrier having an aperture is provided in an electrolyte solution, electrodes are arranged to sandwich the aperture, and subject particles dispersed in the solution are passed through the aperture. When the particle passes through the aperture, an electrical resistance between the electrodes is instantaneously changed and a voltage pulse is generated. The height of the voltage pulse reflects the particle volume, so that a spherical equivalent diameter can be measured regardless of its shape. From the measurement, the volume-based particle size of the sample particles can be obtained. Further, the number of the particles can be counted from the number of the pulses.
In the electrical sensing zone method, the height of the voltage pulse varies depending on a position in the aperture where the particle passes through. Further, a plurality of particles passing together through the aperture may be measured as one particle, or the particles that have passed through the aperture may stay near the aperture and cause noise. To solve these demerits, the sheath flow method has customarily been employed. In a particle size distribution measurement utilizing the sheath flow method, a flow of the particle containing liquid in the flow cell is enclosed with another liquid (sheath liquid) flow to narrow down the particle containing liquid flow so as to introduce the particles in a row into the approximate center of the aperture. Accordingly, the particle size can be obtained with less margin of error.
There is a limitation to the measurable size of the particle in the electrical sensing zone method depending on the diameter of the aperture. For example, where the size of the particle is less than {fraction (1/50)} of the aperture diameter, the signal from the particle is hard to be distinguished from the noise. On the contrary, where the size of the particle is too great, the pulse height and the particle volume lose their linearity, and the aperture tends to be clogged. To replace the flow cell to change the aperture diameter requires removal and attachment of wirings led to the electrodes and pipes connected to the flow cell. Further, where the subject particles have a wide particle size distribution, the measurement will be complicated.
As means to deal with the above demerits, there has been known a measuring apparatus comprising a flow cell which can be divided into two segments and a detecting member sandwiched therebetween, the detecting member having an aperture through which a sheath liquid enclosing a particle containing liquid can pass (for example, see Japanese Unexamined Patent Publication No. HEI 8-15125). The detecting member includes a detachable member sealingly connected to the segments. As the detachable member, both sides of the detecting member are formed each with a thread of the opposite hand so that the detecting member can be removed from the segments by rotating the detecting member only, without rotating the segments.
However, in such a conventional particle measuring apparatus, in the step of attaching the detecting member to the separated segments again, it is difficult to thread both sides of the detector into the segments to the same extent. If one side is tightly threaded before the other side is not threaded enough, the other side loses the watertightness.
The present invention has been achieved in view of the above circumstances, and provides a particle measuring apparatus capable of easy and ensured replacement of the detecting member in the flow cell.
The present invention provides a flow cell for a particle analyzer using an electrical sensing zone method, comprising: a detecting member having a through hole; a first cell for supplying a particle containing liquid to the through hole; a second cell for receiving and discharging the particle containing liquid that has passed through the through hole; electrodes provided in the first cell and the second cell respectively, for supplying an electrical current to the liquid passing through the through hole; and a sliding member for sliding at least one of the first and second cells to change a distance therebetween; wherein the first and second cells cooperate with the sliding member to detachably sandwich the detecting member therebetween so that the detecting member is connected to the first and second cells in a watertight state.
These and other objects of the present application will become more readily apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.